UC Santa Barbara

Herein, we describe a momentum-resolved optical reflectometry technique for precisely quantifying absorption anisotropies, with a particular interest in its ability to estimate distinct out-of-plane dipole strengths in solution-processable semiconductors. We demonstrate major advantages over conventional techniques, e.g., variable-angle spectroscopic ellipsometry, and subsequently show how to merge the strengths of the two techniques. We interrogate two distinct material systems: organic semiconductor thin films and two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs). In organic thin films, we resolve molecular reorientations due to processing conditions. In 2D HOIPs, we adopt a layered effective medium model to show that strong optical anisotropies arise predominantly from classical electromagnetics effects (i.e., dielectric inhomogeneity) rather than anisotropies in the quantum-mechanical matrix elements. Finally, we demonstrate unexpected multipolar light-matter interactions in 2D HOIPs, revealed by a highly polarized and oblique emission sideband. Electromagnetic and quantum-mechanical analyses indicate that this emission originates from an out-of-plane magnetic dipole transition arising from the 2D character of electronic states. The techniques described herein are materials agnostic and may provide insight into fundamental optoelectronic processes and processing-dependent structure-function relationships in a wide variety of interrogated materials.